The invention relates generally to hydraulic systems and more particularly to an improved hydraulic system embodying a demand compensated principle in which the fluid output of a variable displacement pump can be made proportional to the instantaneous pressure demand of one or more fluid motors supplied by the pump.
In the past, the instantaneous demand was sensed by flow changes at the motors and the flow variations were fed back as hydraulic fluid flow to the demand control valve by small pilot lines as in the U.S. Pat. No. 2,892,311 granted to H. W. Van Gerpen on June 30, 1959 and the U.S. Pat. No. 2,892,312 granted to J. R. Allen et al. on June 30, 1959. With the small pilot lines, temperature changes during cold weather would increase the fluid viscosity and thus decrease the flow rate causing substantial problems by decreasing or eliminating the demand compensation response of the system.